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Electra (KrF) Laser Development 16th HAPL Meeting Princeton, New Jersey December 12, 2006 Naval Research Laboratory Plasma Physics Division Washington, DC Presented by M. Wolford Work supported by DOE/NNSA/DP NRL J. Sethian M. Myers J. Giuliani M. Wolford S. Obenschain Commonwealth Tech F. Hegeler M. Friedman T. Albert J. Parrish K. Gunlicks RSI P. Burns R. Lehmberg S. Searles SAIC R. Jaynes Summary Since August HAPL Meeting • Starting Integration of Electra Laser System – First Stages of Construction • Pre-Amplifier Laser Energy Measurements – Increased laser yield to 25 J – Time-Dependent characterization of laser pulse – Near-Field Profile • Cathode & Rep-Rate Durability – Anode Mesh (1st Implementation 12,363 shots) Electra Laser System Main AMP Pre-AMP LPX Electra ISI Source Options Electra ISI Laser Source Options Initial experiments and will continue with LPX as is, non ISI External Cavity f Diffuser w/ additional amplifier f LPX Diffuser A. V. Deniz, S. P. Obenschain Opt. Comm. 106 (1994) 113-122 T. Lehecka et al., Opt. Comm. 117 (1995) 485-491 Amplifier Pinhole Focus See NRL Poster: Large Aperture KrF Discharge Amplifier Electra Laser System Main AMP Pre-AMP Large Amplifier optical architecture LPX Double Pass Large Amp Architecture AMP Large Concave Mirror Closely Packed Convex Mirror Array Amplifier Pinhole Focus Electra Pre-Amplifier Laser Experiments Telescope LPX 305 i 1 cm x 3 cm Cylindrical lens Pair 3 cm x 3 cm Input 0.5 J 10 cm x 10 cm Input Output Calorimeter Review: First light on Electra Pre-Amp 80% Ar, 0.3% Fluorine 30.0 Orestes 0.5 J Input Measured Input ~0.5 J Laser Output (J) 25.0 20.0 15.0 10.0 5.0 0.0 8 12 16 Pressure (psi) 20 25 J Electra Pre-Amplifier Output 30.0 Laser Output (J) 25.0 20.0 15.0 Orestes 0.5 J Input Measured Input ~0.5 J 10.0 Orestes 0.7 J Input Measured Input 0.6 J 5.0 80% Ar, 0.3% F2 0.0 8 12 16 Pressure (psi) 20 Timing Electron Beam to Laser, 10 J Yield Input Output Voltage 5 Diode Voltage Diode Power Output Input Voltage (keV) Power (100 MW) 300 4.5 4 250 3.5 200 3 2.5 150 64.8 ns 2 100 1.5 1 50 0.5 0 -40 -20 0 20 40 60 -50 Time (ns) 80 100 120 0 140 -0.5 Intensity (arb.) 350 Output Time Dependent Intensity 6 1 (-36.3 ns) 3.8 J 4 5 2 (1.3 ns) 10.0 J 5 3 3 (21.5 ns) 15.7 J Intensity (arb.) 4 Output 2 4 (40.7 ns) 20.0 J 5 (64.8 ns) 10.0 J 6 3 6 (88.0 ns) 2.9 J 1 2 Power (10 GW) 1 0 0 20 40 -1 60 80 100 120 140 120 140 Time (ns) 2 1 3 4 5 6 Input -40 -20 0 20 40 60 80 100 Pre-Amplifier Energy Function of Input Timing 25 15 80% Ar, 0.3% F2 @ 16 psi 80%Ar, 0.3% F2 @ 18 psi Orestes 16 psi 10 Orestes 18 psi Energy (J) 20 5 -30 -10 10 30 Time (ns) 50 70 Cause of Discrepancy 90 0 -50 0 50 Input Time (ns) 100 150 Progress in realizing long duration laser runs Previous Limits to Laser Durability (< 10 k shots) March 2006 HAPL meeting primary emitter • Gas buildup in the diode ceramic honeycomb • Degradation of the emitter Solved with new all-carbon emitter. As much as 25 k shots (reported at Aug 2006 meeting) Foil Screen Hibachi • Foil failure due to debris and/or plasma arcs in A-K gap MAY have been solved with high transparency anode screen One Possible mechanism limiting foil durability Electron emission from Anode Hypothesis Rationale Micro particles can stick to the foil Emission is an explosive process. See marks on foil Voltage reverses in diode after the main pulse Seen on Voltage monitors Voltage reversal causes micro particles to emit electrons See what may be "cathode spots" on pressure foil Emission can be an explosive process Known fact. Can puncture hole in highly stressed pressure foil Experiments with an anode foil show evolution of this process First experiments with mesh, (90%-95% effective transmission) show a) Minimal degradation in laser energy (i.e. transmission OK) b) First Implementation lasted several multi-thousand shot runs Summary Since August HAPL Meeting • Starting Integration of Electra Laser System – First Stages of Construction • Pre-Amplifier Laser Energy Measurements – Increased laser yield to 25 J – Time-Dependent characterization of laser pulse – Near-Field Profile • Cathode & Rep-rate Durability – Anode Mesh (1st Implementation 12,363 shots)